Arrangement for duplex operation



Jan. 24, 1939. 1.. DIETRIICH 2,144,336

ARRANGEMENT FQR DUPLEX OPERATION- Filed Feb. 19, 1937 OSC/LZATOR I IWEHIE fluoszrbk 1 LOUD-SPEAKER f 5 z E B L AMPz/F/ER 2 INVENTOR HANS LEODIETRICH KQM ATTORN EY Patented Jan. 24, 1939 UNITED STATES PATENTOFFICE ARRANGEMENT FOR DUPLEX OPERATION tion of Germany ApplicationFebruary 19, 1937, Serial No. 126,618 In Germany January 28, 1936 5Claims.

It is known in the prior art that duplex communication on two difierentwaves is feasible by causing, at both stations, the incoming signal waveto form with the radiated wave an intermediate frequency or beatfrequency.

In the present invention an arrangement is concerned and hereinafterdisclosed which is predicated upon the same principle, but which byvirtue of the use of decimeter or midget waves, according to theinvention, and of the features associated therewith, offers specialmerits both as regards construction and circuit organization.

According to the invention, in a duplex-operation installation utilizingan intermediate or beat frequency obtained by the beating together ofthe incoming wave and the sending wave, decimeter waves are employed insuch a way that a diode rectifier is used for producing the beat ormixing action, while the capacitance of the said rectifier constitutesthe capacity of the oscillation circuit of the receiver system.According to another feature of the invention, an energy feeder line isinterposed between the receiver oscillation circuit and the antenna, theoscillator which serves to generate the outgoing wave being in couplingrelation with the said feeder line (energy lead).

The invention shall now be described in more detail by reference to thesingle figure of the accompanying drawing.

A denotes an antenna which, for example, may comprise several dipoles sothat the action thereof in reference to radiations will bebidirectional. From the antenna a double wire lead B is brought to therectifier G. Parallel to the rectifier is mounted a wire loop D which,acting as an inductance together with the diode capacitance, constitutesthe oscillation circuit of the receiver. It has been discovered that thesaid wire loop may be omitted without any incidental impairment of theperformance. By the provision of two choke-coils Dr, Dr, the decimeterwaves are kept away from the intermediate frequency amplifier Z.Inasmuch as the intermediate frequency potential at the diode G is lowbecause of the low diode resistance, this potential may be stepped up intransformer T. The diode heating voltage is applied by way of chokecoils (not shown). Condenser C only serves to block the way of theintermediate frequency energy to the antenna. Its capacitive reactanceis chosen so low that it will not play any part as far as the decimeterwaves are concerned.

Connected or coupled with the energy feeder lead B is the oscillatorinductance L, being in the form of a tuned Lecher wire line. Inpractice, the said Lecher wire system is disposed at close proximity andparallel to the energy feeder line. The oscillator 0 comprises aself-oscillatory tube, say a magnetron, which is voice-modulated by theway of transformer Tr.

The intermediate frequency part of the circuit is schematicallyindicated at Z, and is tuned to the difference between the outgoing andincoming signal frequencies, and serves to amplify and rectify theintermediate frequency energy. What is only essential is that theamplifier should be designed to handle a very wide frequency band,inasmuch as the intermediate frequency is subject to fluctuationsbecause of inevitable instability of the oscillator wave.

Let us assume, as an example, that the outgoing and the incoming signalfrequencies are 1500 and 1503 megacycles (about cm.) so that thedifference or beat between them is 3 megacycles (100 m. wave). If theoscillator then has an instability factor of l l(lthe beat frequencywill present fluctuations around 1.5megacycles. Under practical workingconditions, a band-width of 1 megacycle suffices, when the beatfrequency is 3 megacycles.

The numerical example hereinbefore cited shows, moreover, that the twosignal waves of 1500 and 1503 megacycles differ only by 2 mils (.2 ofone percent) from each other; in other words, that when the antenna andthe oscillation circuit of the receiver are tuned to one wave, they willbe sharply tuned also to the respective other wave. This is a veryvaluable and essential merit inherent in the arrangement of thisinvention as contrasted with the earlier art. It will be understood thatif duplex trafiic is carried on upon longer waves, the difi'erencebetween the waves expressed in terms of percent, will grow increasinglygreater seeing that the intermediate frequency can not be diminished atwill, in fact, that it must always lie above the highest voice frequencyto be transmitted. The result is that detuning of the aerial and theoscillation circuit in reference to one of the waves must be accepted asinevitable (and this tends to impair the performance and efficiency ofthe scheme), otherwise the antenna and the oscillation circuits willhave to be tuned to different natural frequencies by suitable resonantcircuits. These difficulties are obviated in the arrangement of theinvention here disclosed. As a result the circuit organization usedtherein becomes simple and inexpensive.

Now, in what follows the operation of the arrangement shall bedescribed. In the Lecher wire line L which is tuned to the sending oroutgoing signal frequency, waves are produced which are transferred tothe energy feeder lead B. Part of the oscillations is to be fed to thediode G in order to be beaten therein with the incoming signal waves,though by far the largest part of the generated energy is to be radiatedout through the aerial;

The relationship between the radiated and the rectified energy (i. e.,radiation resistance of the antenna and the rectifier resistance) may becalculated from the ratio of the two terminal resistances (impedances)of the energy lead. In order that so far as the energy to be transmittedis concerned, there may be no reflection point in the aerial, the energyfeeder lead B must be matched; in other words, the characteristicimpedance of the feeder B must be like that of the antenna. Feeder B ismatched to antenna A, but a considerable mismatch is arranged to occurat the diode. Hence energy fed into feeder B from L goes mostly outwardto the antenna as radiation, the energy reaching the diode being mostlyreflected and preferably reflected in such phase as to reinforce thewaves traveling to antenna A. Of course, this means that for receivingpurposes the energy is not most efficiently absorbed by the diode butthis drawback is tolerable in view of the use of high frequencyamplification and the other merits of the arrangement. The unmatchedimpedance of the diode oscillatory circuit, which for the resonancefrequency is equal to the internal impedance of the diode, governs theportion or fraction of the oscillator energy which will be fed to therectifier. In order that the entire balance of the said energy may beradiated, care will have to be taken so that the oscillations which arereflected at the diode will be fed in phase with the oscillations comingfrom the generator, to the antenna. This is effected by an exactregulation of the length of the energy feeder line. In the presence ofperfect coincidence of phases, it will be seen that the reflected andthe direct waves will boost one another and will be radiated conjointly.

To be sure, part of the incoming Waves will be reflected also at thediode. Mowever, since the diode impedance is comparatively low comparedto the anti-resonant impedance of the terminals of the energy feeder,and the sensitiveness of the arrangement is made comparatively greatbecause of the fact that the beat reception principle is used, this lossin reception may be readily tolerated in the light of the other valuableoperating advantages inhering in the scheme.

The diode oscillation circuit itself need not be tuned throughout a widewave band seeing that its resonance curve is extremely broad because ofthe internal diode resistance. If it is tuned on the average to 20 cm.wavelength, it will be understood that a change to a 19 cm. or a 21 cm.wave will not entail any practical efiects. But this means a frequencyrange of around megacycles inside which from 30 to 40 duplex equipmentswith intermediate frequencies of 3 megacycles may be received withoutany special tuning of the receiver oscillation circuit. This wide waveband is one of the advantages of the invention which, however, hasbecome utilizable in practice only since the adoption of the decimeterwaves.

The arrangement as hereinbefore disclosed in most instances will besuperfluous.

may be perfectly accommodated with batteries, intermediate frequencyamplifiers, and, if desired, an audio frequency amplifier, etc., insidea shielded case of reduced dimensions, with the aerial being mountedoutside the shielding means, preferably on the box itself. To operatethe equipment, only one knob need be used for tuning and other purposes.If necessary, also, the coupling between the energy feeder line and theoscillator could be made variable, say by pivoting the oscillatorinductance so as to be positioned at greater or 'less proximity, thoughthis On connecting the arrangement, first a buzzer or the like could beused to modulate the outgoing signal wave. In the headset the buzzernote of the installation will be heard only when the correspondentstation has been accurately tuned, for it will be only then that anintermediate frequency modulated by the buzzer soundwill be formed. Butas soon as the buzzer sound becomes audible, the microphone may beconnected, whereupon conversation may be started.

What is claimed is:

1. An ultra short wave duplex communication system for the transmissionand reception of waves below one meter, including a radiating elementfor radiating extremely short waves, a transmitting oscillator, a signalinput circuit coupled to said oscillator for modulating the 0scillationsgenerated thereby, a tuned circuit coupled to the output of saidoscillator, said tuned circuit, in turn, being coupled to said radiatingelement, and a receiving circuit including an intermediate frequencyamplifier also coupled to said radiating element, said receiving circuitcomprising an oscillatory circuit tuned to the oscillator and receivedfrequencies, said intermediate frequency amplifier functioning toreceive a frequency substantially equal tothe difference between thefrequency of said oscillator and the frequency of the incoming signalsreceived by said radiating element, said last oscillatory circuitcomprising a diode rectifier whose interelectrode capacitanceconstitutes the capacity of said oscillatory circuit, and means locatedbetween said intermediate frequency amplifier and said last oscillatorycircuit for preventing the passage of waves having the frequency of saidincoming signals or of said oscillator to said amplifier.

2. An ultra short wave duplex communication system for the transmissionand reception of waves below one meter, including a radiating elementfor radiating extremely short waves, a continuously operatingtransmitting oscillator generating waves below one meter, a signal inputcircuit coupled to said oscillator for modulating the oscillationsgenerated thereby, an output circuit for said oscillator comprising atuned Lecher wire system, a receiving system including an intermediatefrequency producing oscillation detector and an intermediate frequencyam plifier connected to said oscillation-detector, a parallel-wirefeeder line extending between said oscillation-detector and saidradiating element, said output circuit for said transmitting oscillatorbeing electromagnetically coupled to said feeder line, said oscillationdetector comprising a diode coupled across said feeder line, theinterelectrode capacitance of said diode forming the capacitance of anoscillatory circuit tuned to the oscillator and received frequencies.

3. An ultra short wave duplex communication system for the transmissionand reception of Waves below one meter, including a radiating elementfor radiating extremely short waves, a continuously operatingtransmitting oscillator generating waves below one meter, a signal inputcircuit coupled to said oscillator for modulating the oscillationsgenerated thereby, an output circuit for said oscillator comprising atuned Lecher Wire system, a receiving system including an intermediatefrequency producing oscillation detector and an intermediate frequencyamplifier connected to said oscillation detector, a parallelwire feederline extending between said oscillation detector andrsaid radiatingelement, said output circuit for said transmitting oscillator beingelectromagnetically coupled to said feeder line, said oscillationdetector comprising a diode coupled across said feeder line, theinterelectrode capacitance of said diode forming the capacitance of anoscillatory circuit tuned to the transmitting and received frequencies,said parallelwire feeder line having such length and dimensions that theimpedance at the terminals thereof, which are coupled to said radiatingelement, matches the surge impedance of said radiating element, and thewaves reflected at the terminals of said line which are connected tosaid detector will be in phase with the waves of transmitting oscillatorfrequency which travel toward said radiating element.

4. An ultra short wave duplex communication system for the transmissionand reception of waves below one meter, including a radiating elementfor radiating extremely short waves, a continuously operatingtransmitting oscillator generating waves below one meter, a signal inputcircuit coupled to said oscillator for modulating the oscillationsgenerated thereby, an output circuit for said oscillator comprising atuned Lecher wire system, a receiving system including an intermediatefrequency producing oscillation detector and an intermediate frequencyamplifier connected to said oscillation detector, a parallel-Wire feederline extending between said oscillation detector and said radiatingelement, said output circuit for said transmitting oscillator beingelectromagnetically coupled to said feeder line, said oscillationdetector comprising a diode coupled across said feeder line, theinterelectrode capacitance of said diode forming the capacitance of anoscillatory circuit tuned to the transmitting frequency, saidoscillatory circuit being also tuned to receive an incoming Wave belowone meter, which incoming wave has a frequency differing by less thanone percent from the oscillation frequency of said transmittingoscillator.

5. An ultra short wave communication system for the transmission andreception of waves below one meter, comprising an oscillatory circuitfor resonating the received wave, and a local oscillator for producingboth the wave to be transmitted and the mixing wave, said oscillatorycircuit having a diode rectifier for mixing the received wave and theWave generated by said local oscillator to produce the intermediatefrequency wave, the capacitance of said diode forming the capacitance ofsaid oscillatory circuit.

HANS LEO DIETRICH.

